1. Field of the Invention
The present invention relates to a dual antenna device, and more particularly, to a low profile concentric dual antenna device.
2. Description of the Prior Art
With the global positioning system (GPS) technology maturity and the public demand for mobile communications, an automotive satellite communication device, such as a satellite navigation device, a satellite radio, etc, is popular in a daily life. In general, antennas of different automotive satellite communication devices are separately installed. Therefore, if a user wants to use the satellite navigation device and the satellite radio at the same time, two antennas are required to be installed independently, which waste not only space but also affect the appearance of the automobile.
Therefore, the prior art provides several solutions for integrating two antennas into a single antenna device. Please refer to FIGS. 1A and 1B, which are a cross-sectional diagram and a vertical view diagram of a dual antenna device 10 respectively. The dual antenna device 10 is composed of side by side antennas A1 and B1, where the antenna A1 includes a radiating unit 100A, a substrate 102A, and a feeding unit 104A, and the antenna B1 includes a radiating unit 1008, a substrate 1028, and a feeding unit 1048. The substrate 102A and 1028 can be materials as ceramic, substrate of a printed circuit board, etc. In addition, a grounding unit 106 is a common ground of the antennas A1 and B1. As can be seen in FIGS. 1A and 1B, the grounding unit 106 of the dual antenna device 10 is rectangular and is not symmetric, which causes differences in radiating field patterns of two perpendicular cross-sectional directions. The radiating field pattern with longer ground is more concentrated than the other, and an isolation problem occurs if the antennas A1 and B1 are too close. In addition, a shape for the rectangular dual antenna device 10 is difficult to design.
Please refer to FIGS. 2A and 2B, which are a cross-sectional diagram and a vertical view diagram of a dual antenna device 20 according to the prior art respectively. The dual antenna device 20 is composed of superposed antennas A2 and B2, where the antenna A2 includes a radiating unit 200A, a substrate 202A, and a feeding unit 204A, and the antenna B2 includes a radiating unit 200B, a substrate 202B, and a feeding unit 204B. In addition, a grounding unit 206 is a common ground of the antennas A2 and B2. In the dual antenna device 20, radiating field patterns of the antennas A2 and B2 are symmetric, but the feeding unit 204A of the upper antenna A2 placed through a resonator of the lower antenna B2 causes an isolation problem between the two antennas. In addition, a height of an appearance of the dual antenna device 20 increase affects the appearance of the dual antenna device 20. As abovementioned, the conventional dual antenna devices are needed to be improved in ways of radiating field, isolation, appearance, etc.